Almost 100 new cases were reported in China, the largest increase in more than a month.A study of a drug, related to the one President Trump has promoted, was halted after several patients developed potentially fatal heartbeat irregularities.

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Hokkaido, Japan’s northernmost island, declared a state of emergency for a second time after a new wave of cases there.

Erdogan rejected the resignation of the minister who oversaw Turkey’s rushed lockdown.

President Recep Tayyip Erdogan declined on Sunday to accept the resignation of Turkey’s interior minister, who offered it after taking responsibility for an abruptly announced curfew over the weekend that set off panic buying.

The minister, Sulyeman Soylu, announced his resignation late Sunday on Twitter, saying that he was responsible for implementing the lockdown. Within an hour, the president’s director of communications announced that Mr. Erdogan had refused to accept his resignation.

Mr. Soylu is one of the most powerful ministers of Mr. Erdogan’s cabinet, and his attempted resignation, following the removal of another minister two weeks ago, is an indication of the political fallout of the coronavirus pandemic.

Confirmed cases have risen to more than 56,000 in Turkey’s population of 80 million, and deaths are at 1,198.

The lockdown for 31 provinces was announced just two hours before it went into force at midnight on Friday, sending thousands of citizens rushing to late-night stores to buy provisions, undoing the government’s efforts to encourage social distancing.

At the time, Mr. Soylu said the lockdown was ordered by the president, but on Sunday, he said, that the responsibility for “implementing the weekend curfew decision, which was aimed at preventing the epidemic, belongs entirely to me.”

Turkey had seemed to be controlling the spread of the virus better than some European nations, and Mr. Erdogan introduced gradual restrictions while keeping some businesses working. The country was suffering double-digit unemployment and inflation even before the pandemic began.

Mr. Erdogan has sought to reassure citizens that the government will manage the health and financial fallout of the pandemic, but complaints are rising that a government compensation plan is inadequate. Many casual laborers are without income, and thousands of workers are being laid off.

An unexpected new source of coronavirus infections in China has emerged: Russia.

A surge of Chinese people returning from Russia, which is now experiencing its own spike in infections, has fueled the largest increase in reported new cases in China in more than a month.

Chinese officials said on Monday that 98 new infections were reported among people who recently arrived in China. The overwhelming majority of those were Chinese citizens, apparently scrambling to return to their homeland after China strictly limited flights in and out of the country.

Previously, an Aeroflot flight from Moscow to Shanghai on April 10 carried 60 people who ultimately tested positive for the coronavirus. The passengers have all been forced into government quarantine.

That flight arrived just days after China announced that it would close, effective Monday, its last overland crossing at Suifenhe, a small city across the border from Primorsky Krai, a region in Russia’s Far East.

Many Chinese people seeking to flee Russia have flown from Moscow to Vladivostok in hopes of completing the last leg by land. The Chinese Consulate in Vladivostok said in a statement on Sunday that 243 Chinese citizens infected with the coronavirus had already crossed the border. So many cases have emerged in the borderlands that the local government has opened a temporary hospital to deal with the caseload.

Russia closed its borders with China in January, hoping to staunch the spread of the pandemic, only to find itself facing a belated spike in cases. By Monday, Russia had nearly 16,000 cases and at least 130 deaths.

A Japanese island declared a state of emergency for a second time.

In an example of how initial successes of a social distancing campaign can fade once restrictions are relaxed, Hokkaido, Japan’s northernmost island, declared a state of emergency for a second time on Sunday and called on residents to stay at home for all but the most essential outings.

Hokkaido’s governor, Naomichi Suzuki, said the government was taking action because of a second wave of infections. Long before Japan’s central government issued a state of emergency for the country’s seven largest prefectures last week, Hokkaido independently called for a soft lockdown of the region on Feb. 28. As cases appeared to come under control, the prefecture lifted the state of emergency on March 19 and slowly allowed schools to reopen.

Overall case numbers are still low in Hokkaido, but the government is concerned about how quickly they are multiplying. Four new cases were confirmed on April 7, and had tripled within five days to 12.

On Sunday, Hokkaido and Sapporo, the provincial capital, asked residents to refrain from going out, cease traveling and avoid restaurants — particularly for “business entertainment.” All schools in Sapporo will also be closed from April 14 through May 6.

In Osaka, Japan’s third largest city, the governor requested on Monday that a range of businesses including night clubs, internet cafes, karaoke venues, pachinko parlors, movie theaters, gyms, museums and libraries close until May 6.

The governor, Hirofumi Yoshimura, said he was asking businesses to close “to prevent an explosive expansion of infections in Osaka.” The move followed similar requests in Tokyo. Under the law authorizing the state of emergency, governors have the power only to request that businesses close. Those who do not comply can be publicized, but not officially punished.

Japan’s health ministry reported 530 new cases and four deaths on Sunday, taking Japan’s total to 7,255 cases and 102 deaths.

In Tokyo, the city reported 166 new cases on Sunday, more than half of which were concentrated in one hospital in the Nakano ward of the city. Both patients and staff members were infected. The Nakano hospital’s infections were the latest of several recent clusters reported at hospitals in Japan.

A chloroquine study ends in Brazil over concerns of fatal heart complications.

A small study of chloroquine, which is closely related to the hydroxychloroquine drug President Trump has enthusiastically promoted, was halted in Brazil after coronavirus patients taking a higher dose developed irregular heart rates that increased their risk of a potentially fatal arrhythmia.

The study involved 81 hospitalized patients in the city of Manaus and was sponsored by the Brazilian state of Amazonas. Roughly half the study participants were given a dose of 450 milligrams of chloroquine twice daily for five days, while the rest were prescribed a higher dose of 600 milligrams for 10 days. Within three days, researchers started noticing heart arrhythmias in patients taking the higher dose. By the sixth day of treatment, 11 patients had died, leading to an immediate end to the high-dose segment of the trial.

“To me, this study conveys one useful piece of information, which is that chloroquine causes a dose-dependent increase in an abnormality in the E.C.G. that could predispose people to sudden cardiac death,” said Dr. David Juurlink, an internist and the head of the division of clinical pharmacology at the University of Toronto, referring to an electrocardiogram, which reads the heart’s electrical activity.

The researchers said the study did not have enough patients in the lower-dose portion of the trial to conclude if chloroquine was effective in patients with severe cases of Covid-19, the disease caused by the coronavirus. More studies evaluating the drug earlier in the course of the disease are “urgently needed,” the researchers said.

Despite its limitations, infectious disease doctors and drug safety experts said the study provided further evidence that chloroquine and hydroxychloroquine, which are both used to treat malaria, can pose significant harm to some patients, specifically the risk of a fatal heart arrhythmia. Patients in the trial were also given the antibiotic azithromycin, which carries the same heart risk. Hospitals in the United States are also using azithromycin to treat coronavirus patients, often in combination with hydroxychloroquine.

President Trump has enthusiastically promoted them as a potential treatment for the novel coronavirus despite little evidence that they work, and despite concerns from some of his top health officials. Companies that manufacture both drugs are ramping up production.

The Israeli spy service has helped the country obtain coveted medical supplies.

Israel’s powerful spy service has been deeply involved in the country’s fight against the coronavirus, and has been one of its most valuable assets in acquiring medical equipment and manufacturing technology abroad, according to Israeli medical and security officials.

As countries around the world compete ferociously for limited supplies during the pandemic, they are turning to any help available, and flexing their muscles unapologetically.

And with the Mossad having determined that Iran — struggling with its own coronavirus crisis — no longer represents an immediate security threat, the agency could afford to immerse itself in the health emergency, according to multiple people knowledgeable about its operations.

In early March, a command and control center was set up to handle the distribution of medical gear across the country, with Yossi Cohen, the Mossad chief, at its head and headquartered at Sheba Medical Center, Israel’s biggest hospital.

Professor Yitshak Kreiss, Sheba’s director general, said the Mossad had been pivotal in helping Sheba secure vital medical equipment and expertise from abroad.

Professor Kreiss declined to say precisely how Mossad officers had helped the Israeli medical establishment or where the imported equipment came from. But according to six current or former Israeli officials with knowledge of the Mossad’s operations, the agency used international contacts to avert shortages that might have overwhelmed Israel’s health system.

Britain surpasses 10,000 deaths, and Boris Johnson is released from the hospital.

In Britain, where the total number of reported coronavirus deaths surpassed 10,600 this weekend, Prime Minister Boris Johnson was released from the hospital on Sunday.

It was a major step forward in his recovery from the coronavirus and a welcome relief for a nation whose political leadership has been harder hit by the contagion than that of any other Western country.

In a video posted on Twitter, he credited the National Health Service with saving his life, calling it “the beating heart of this country.”

“It’s hard to find words to express my debt,” he said, looking a bit wan but speaking with his usual vigor.

He thanked Britons for adhering to social distancing measures and said they were helping to slow the spread of the virus.

Mr. Johnson, who spent three nights in intensive care at St. Thomas’ Hospital in London, will convalesce at Chequers, the prime minister’s country house, the government said in a statement. But he will soon be able to sign off on major decisions, including when to ease the country’s lockdown.

His release came a day after Queen Elizabeth II released a recorded Easter message in which she said that the holiday was a time of “light overcoming darkness.”

“We know that coronavirus will not overcome us,” the queen said. “As dark as death can be, particularly for those suffering with grief, light and life are greater. May the living flame of the Easter hope be a steady guide as we face the future.”

The total number of confirmed cases in the country is nearly 79,000, and the virus has also emerged in the country’s prisons.

Flight attendants and pilots question whether they should still be working.

Airlines have canceled a staggering number of flights, but thousands still take off every day, leaving many of the people needed to keep them running to reckon with whether to continue working and how to stay safe if they do.

Already, hundreds of flight attendants and pilots have fallen ill and at least five have died from the coronavirus, according to to the labor unions that represent them.

Tens of thousands of airline employees have taken unpaid leave, staying home out of necessity or concern or to free up slots for colleagues who may need the income more. But some have continued to show up reluctantly, either because they need the money or fear losing their jobs once the crisis has ebbed.

Flight attendants and pilots at several major airlines, many of whom requested anonymity for fear of losing their jobs, said they have had to take their own gloves and masks to work. Even when airlines have committed to providing protective equipment, many have run into the same supply problems that have plagued hospitals across the country.

Air travel has fallen to new lows: For the first time since its formation, the Transportation Security Administration screened fewer than 100,000 people at its checkpoints. It screened more than two million people on the same day last year.

The plan was delayed after the lone holdout, Mexico, stood firm on its position to cut 100,000 barrels a day and not the 400,000 barrels that Saudi Arabia had pushed for. The United States, Brazil and Canada promised to make up the 300,000-barrel-a-day difference.

The collapse in economic activity caused by the virus reduced demand by an estimated 30 million to 35 million barrels a day, according to international energy agencies and oil consultants. Analysts expect oil prices, which soared above $100 a barrel only six years ago, to remain below $40 for the foreseeable future.

Russia and Saudi Arabia — which only a month ago hoped to undercut American producers — have retreated from threats to pump more oil into the already-saturated market. PresidentTrump had lobbied both countries to lower production.

When will this end?

This is a difficult question, because a lot depends on how well the virus is contained. A better question might be: “How will we know when to reopen the country?” In an American Enterprise Institute report, Scott Gottlieb, Caitlin Rivers, Mark B. McClellan, Lauren Silvis and Crystal Watson staked out four goal posts for recovery: Hospitals in the state must be able to safely treat all patients requiring hospitalization, without resorting to crisis standards of care; the state needs to be able to at least test everyone who has symptoms; the state is able to conduct monitoring of confirmed cases and contacts; and there must be a sustained reduction in cases for at least 14 days.

What should I do if I feel sick?

If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor. They should give you advice on whether you should be tested, how to get tested, and how to seek medical treatment without potentially infecting or exposing others.

Should I wear a mask?

The C.D.C. has recommended that all Americans wear cloth masks if they go out in public. This is a shift in federal guidance reflecting new concerns that the coronavirus is being spread by infected people who have no symptoms. Until now, the C.D.C., like the W.H.O., has advised that ordinary people don’t need to wear masks unless they are sick and coughing. Part of the reason was to preserve medical-grade masks for health care workers who desperately need them at a time when they are in continuously short supply. Masks don’t replace hand washing and social distancing.

How does coronavirus spread?

It seems to spread very easily from person to person, especially in homes, hospitals and other confined spaces. The pathogen can be carried on tiny respiratory droplets that fall as they are coughed or sneezed out. It may also be transmitted when we touch a contaminated surface and then touch our face.

Is there a vaccine yet?

No. Clinical trials are underway in the United States, China and Europe. But American officials and pharmaceutical executives have said that a vaccine remains at least 12 to 18 months away.

What makes this outbreak so different?

Unlike the flu, there is no known treatment or vaccine, and little is known about this particular virus so far. It seems to be more lethal than the flu, but the numbers are still uncertain. And it hits the elderly and those with underlying conditions — not just those with respiratory diseases — particularly hard.

What if somebody in my family gets sick?

If the family member doesn’t need hospitalization and can be cared for at home, you should help him or her with basic needs and monitor the symptoms, while also keeping as much distance as possible, according to guidelines issued by the C.D.C. If there’s space, the sick family member should stay in a separate room and use a separate bathroom. If masks are available, both the sick person and the caregiver should wear them when the caregiver enters the room. Make sure not to share any dishes or other household items and to regularly clean surfaces like counters, doorknobs, toilets and tables. Don’t forget to wash your hands frequently.

Should I stock up on groceries?

Plan two weeks of meals if possible. But people should not hoard food or supplies. Despite the empty shelves, the supply chain remains strong. And remember to wipe the handle of the grocery cart with a disinfecting wipe and wash your hands as soon as you get home.

Should I pull my money from the markets?

That’s not a good idea. Even if you’re retired, having a balanced portfolio of stocks and bonds so that your money keeps up with inflation, or even grows, makes sense. But retirees may want to think about having enough cash set aside for a year’s worth of living expenses and big payments needed over the next five years.